<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <div class="input_num">
            <button @click='down'>-</button>
            <span>{{ num }}</span>
            <button @click='up'>+</button>
        </div>
        
    </div>
    
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <script>
        var app = new Vue({
            el:'#app',
            data:{
                num:1
            },

            methods:{
                down(){
                    if(this.num>0){
                        this.num--;
                    }else{
                        alert('这已经到底了')
                    }
                },

                up(){
                    if(this.num<10){
                        this.num++; 
                    }else{
                        alert('这是我的上线')
                    }
                }
            }
        })
    </script>
</body>
</html>